Diabetic macular edema-like ocular lesions in male spontaneously diabetic torii fatty rats

Protective Effect of Pemafibrate Treatment against Diabetic Retinopathy in Spontaneously Diabetic Torii Fatty Rats

Diabetic retinopathy (DR) can cause visual impairment and blindness, and the increasing global prevalence of diabetes underscores the need for effective therapies to prevent and treat DR. Therefore, this study aimed to evaluate the protective effect of pemafibrate treatment against DR, using a Spontaneously Diabetic Torii (SDT) fatty rat model of obese type 2 diabetes. SDT fatty rats were fed either a diet supplemented with pemafibrate (0.3 mg/kg/day) for 16 weeks, starting at 8 weeks of age (Pf SDT fatty: study group), or normal chow (SDT fatty: controls). Normal chow was provided to Sprague-Dawley (SD) rats (SD: normal controls). Electroretinography (ERG) was performed at 8 and 24 weeks of age to evaluate the retinal neural function. After sacrifice, retinal thickness, number of retinal folds, and choroidal thickness were evaluated, and immunostaining was performed for aquaporin-4 (AQP4). No significant differences were noted in food consumption, body weight, or blood glucose level after pemafibrate administration. Triglyceride levels were reduced, and high-density lipoprotein cholesterol levels were increased. Extension of oscillatory potential (OP)1 and OP3 waves on ERG was suppressed in the Pf SDT fatty group. Retinal thickness at 1,500 microns from the optic disc improved in the Pf SDT fatty group. No significant improvements were noted in choroidal thickness or number of retinal folds. Quantitative analyses showed that AQP4-positive regions in the retinas were significantly larger in the Pf SDT fatty group than in the SDT fatty group. The findings suggest that pemafibrate treatment can exert protective effects against DR.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Effects of natural dihydrochalcones in sweet tea (Lithocarpus polystachyus) on diabetes: a systematical review and meta-analysis of animal studies

Sweet tea (Lithocarpus polystachyus Rehd.), a natural functional food highly rich in dihydrochalcones including trilobatin, phlorizin and phloretin, is reported to possess numerous biological activities especially for treating diabetes. Here, the aim of this systematical review and meta-analysis is to assess the effect of dihydrochalcones in sweet tea (DST) on diabetes and summarize their possible mechanisms. We searched in eight databases including Embase, PubMed, Cochrane, Web of Science, WanFang database, VIP database, China National Knowledge Infrastructure and China Biology Medicine from Jan 2000 to Nov 2021 and ultimately included 21 animal studies in this review. A total of 10 outcome measurements including blood lipid indexes, blood glucose, insulin resistance indicators and oxidative stress biomarkers were extracted for meta-analysis using RevMan 5.4 software. DST significantly decreased the levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), blood glucose (BG), homeostasis model assessment of insulin resistance (HOMA-IR) and malondialdehyde (MDA), and increased high-density lipoprotein cholesterol (HDL-c), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity in diabetic animal models. In summary, DST could treat diabetes by regulation of blood glucose/lipid metabolism, oxidative/carbonyl stress, inflammatory response etc.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Glomerular hyperfiltration with hyperglycemia in the spontaneously diabetic Torii (SDT) fatty rat, an obese type 2 diabetic model

Glomerular hyperfiltration is observed in an early stage of kidney diseases including diabetic nephropathy. A better understanding of pathophysiological changes in glomerular hyperfiltration is essential for development of new therapies to prevent kidney disease progression. In this study, we investigated glomerular changes including glomerular filtration rate (GFR) and glomerular size in the Spontaneously Diabetic Torii (SDT) fatty rat, an obese type 2 diabetic model, and we also evaluated pharmacological effects of the sodium glucose cotransporter 2 inhibitor dapagliflozin on the renal lesions. Dapagliflozin was administered to SDT fatty rats from 5 to 17 weeks of age. Blood and urinary biochemical parameters were periodically measured. GFR was determined by transdermal GFR monitor at 16 weeks of age and histopathological analysis was performed at 17 weeks of age. SDT fatty rat developed severe hyperglycemia and exhibited pathophysiological abnormalities in the kidney, such as an increased GFR, glomerular hypertrophy and tissue lesions. Dapagliflozin achieved good glycemic control during the experimental period, inhibited the increase in GFR, and improved histopathological abnormalities in tubules. These results suggest that the SDT fatty rat is a useful model for analyzing the pathogenesis of diabetic nephropathy during its early stage and dapagliflozin improves not only hyperglycemia but also glomerular hyperfiltration and tubule lesions in SDT fatty rat.

Diabetic Cataract in Spontaneously Diabetic Torii Fatty Rats

Spontaneously Diabetic Torii (SDT) fatty rat is a novel animal model of type 2 diabetes with obesity. SDT fatty rats develop hyperglycemia, dyslipidemia, and other diabetic complications including ocular disorders; however, diabetic cataract formation in SDT fatty rats has not been fully investigated. The aim of the current study was to investigate the characteristics of cataract in the SDT fatty rats. The mean body weight of SDT fatty rats is larger than that of age-matched Sprague-Dawley (SD) rats and control animals until 8 weeks of age, and thereafter the growing speed decreased until the end of observation at 16 weeks of age. Blood glucose levels in SDT fatty rats were significantly higher than those in SD rats throughout the observational period. Slit-lamp examination revealed that no rats showed cataract formation at 5 weeks of age; however, SDT fatty rats gradually developed cortical cataract and posterior subcapsular cataract, both of which are the common types of cataract in patients with type 2 diabetes. The levels of glucose, sorbitol, and fructose were higher in the lens tissues of SDT fatty rats in comparison with that of SD rats. Furthermore, the level of 4-hydroxynonenal (4-HNE) was higher in the lens of SDT fatty rats than in that of SD rats. By contrast, total glutathione (GSH) concentration was lower in the lens of SDT fatty rats than in that of SD rats. The present study demonstrated that the cataractogenesis in SDT fatty rats resembled human diabetic cataract formation, indicating that SDT fatty rats serve as a potential animal model in researches on human cataract associated with type 2 diabetes and obesity.

Pathological Features of Diabetic Retinopathy in Spontaneously Diabetic Torii Fatty Rats

OBJECTIVE

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele (obesity gene) of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. We studied the pathologic features of diabetic retinopathy (DR) in this animal.

METHODS

The eyes of SDT fatty, SDT (controls), and Sprague Dawley (SD) rats (normal controls) were enucleated at 8, 16, 24, 32, and 40 weeks of age (n = 5-6 for each rat type at each age). The retinal thicknesses, numbers of retinal folds, and choroidal thicknesses were evaluated. Immunostaining for glial fibrillary acidic protein (GFAP) and vascular endothelial growth factor (VEGF) was performed. Quantitative analyses of the immunopositive regions were performed using a cell-counting algorithm.

RESULTS

The retinas tended to be thicker in the SDT fatty rats and SDT rats than in the SD rats; the choroids tended to be thicker in the SDT fatty rats than in the SD rats. The retinal folds in the SDT fatty rats developed earlier and were more severe than in the SDT rats. Quantitative analyses showed that the GFAP- and VEGF-positive regions in the retinas of the SDT fatty rats were significantly larger than those of the SDT rats.

CONCLUSIONS

SDT fatty rats developed more severe DR earlier than the SDT rats. The SDT fatty rats might be useful as a type 2 diabetes animal model to study DR.